1. Field of the Invention
The present invention relates to a system for the venting of a liquid tank.
2. Description of the Related Art
The present invention relates to a system for the venting of a liquid tank.
Liquid tanks, when liable to be displaced together with the liquid which they contain, are usually equipped with a ventilation system ensuring environmental safety when the tank is subjected to various stresses: movements in all directions and of any amplitude, thermal stresses, pressure drops or excess pressures.
This requirement is applicable to fuel tanks, particularly when they are mounted on motor vehicles, and when it is essential to prevent liquid fuel from escaping and to control the pronounced changes in gas pressure and volume during filling and for the entire duration of storage in the tank.
Solutions for solving these problems have been developed, making use of safety valves which are submerged in the tank and the upper part of which passes through a wall of the latter. These valves usually open onto a pipe leading to a housing or canister containing a material capable of trapping the liquid vapours present in the gases coming from the tank. It is not uncommon, however, for systems of this type still to present difficulties because, due to the special circumstances occurring during use, such as sudden movements or excessive inclination of the vehicle, liquid coming from the tank may nevertheless pass through the barrier of the safety valve and be present in the pipe leading to the canister, even reach the latter and disturb the free passage of the vapours.
To remedy this accidental entrainment of liquid out of the tank, attempts have been made to retain the liquid, which would escape through the pipe leading to the canister, by inserting into this pipe a dead volume intended to act as a capacity for collecting the liquid and allowing the vapours to pass freely.
Moreover, when it is not possible for them to be integrated into the safety valve itself, safety devices ensuring the prevention of overfilling of the tank (an xe2x80x9cISRxe2x80x9d device wherein ISR stands for the French xe2x80x9cIntediction de Surxe2x80x94Remplissagexe2x80x9d) and for the automatic closing of the latter in the event of overturning (xe2x80x9cROVxe2x80x9d device or roll-over valve) also have to be mounted on the tank or in its immediate surroundings. Multiple pipelines then connect the valve, the ISR and ROV devices and the canister to one another. These pipelines and the numerous connections which they require are often the source of microleaks which are unacceptable in view of the EURO 2000 programme and aims for the drastic reduction of emissions. It is also not uncommon for these multiple pipelines to have low points and siphons, in which small quantities of liquid accumulate and form as many obstacles to the free passage of the gases.
It is known, from British patent application GB-A-2,269,375, to use a capacity which has leaktight walls and is integrated within a fuel tank and in which a safety valve is housed (see FIG. 2). A calibrated orifice 14 made at the top of the capacity allows the liquid to enter in the event of excessive inclinations or excessively violent movements of the tank. A duckbill-shaped non-return valve 12 makes it possible to empty the capacity 11 when the level of the liquid has fallen.
In this system, however, there are still problems associated with the inopportune closing of the valve and with the increase in pressure in the tank which may disturb the smooth operation of the engine. Moreover, when liquid droplets of small size are entrained via the orifice 14, they may, because of their low weight, be entrained directly towards the venting line 7 by the gas stream, without falling into the capacity 11. Furthermore, the ISR and ROV devices must still be connected to the valve with the aid of lines external to the tank.
The object of the invention is to overcome the disadvantages of the known ventilation systems by providing a system which avoids a capacity being placed on the lines external to the tank, makes it possible to empty out the liquid retained in the capacity in the event of a fall in the liquid level in the tank, conforms to the most stringent environmental standards and does not bring about any excess pressure inside the tank.
For this purpose, the invention relates to a system for the venting of a liquid tank, comprising, on the one hand, a float valve arranged in the tank, in communication with a venting pipe, and, on the other hand, a closed volume internal to the tank and provided with an emptying device, the said volume acting as a capacity intended for collecting and retaining any possible entrainments of liquid coming from the tank, according to which this float valve is located outside the volume of the capacity and is connected to the latter by means of the pipe of the venting circuit.
Preferably, the venting pipe in communication with the valve forms one end of a venting circuit. There may be a single venting circuit or, on the contrary, a plurality of these. Even more preferably, this pipe forms the end of the single venting circuit.
The liquid tank is a closed containment, of various shapes, which is generally leaktight relative to the outside and which may be equipped with various internal accessories or accessories passing through the wall of the containment. The tank may contain any type of organic or inorganic liquid or any mixture of such liquids. In particular, it is a fuel tank for motor vehicles. All the types of fuel used by motor vehicles may be stored in the liquid tank, in particular petrol and gas oil.
The system for the venting of a liquid tank, which is the subject of the invention, is a device comprising a plurality of elements, the overall function of which is to make it possible to degas a tank during the filling of the latter and to ventilate it during the period of use and consumption of the liquid which it contains, whilst keeping its external surroundings protected from any leak or emanation of undesirable gases.
The venting system according to the invention comprises a float valve, that is to say a device making it possible to open the tank with the aid of a valve controlled by the displacement of a float driven by the liquid level present in the tank.
According to the invention, the float valve is arranged completely within the tank.
Alternatively, the float valve may also be arranged in the tank and have an upper part which passes through a wall of this tank. The passage of the upper part of the valve through the wall of the tank is carried out under leaktight conditions by means of any suitable technique which is well-known per se. As an example of a leaktightness technique which may be used, mention may be made in a non-limiting way of the welding of the upper part of the valve to the cut-out wall of the tank, leaktight clamping or the use of a gasket designed for the type of liquid contained.
In the venting system according to the invention, the valve upper part emerging from the wall of the tank is in communication with a pipe which forms one end of a venting circuit. In other words, the gases emerging from the tank or entering the latter circulate in this pipe which, on one side, is connected in a leaktight manner to the valve upper part opening onto the valve actuated by the float and, on the other side, communicates with a circuit terminating in the outside atmosphere.
According to the invention, the venting system also comprises a closed volume internal to the tank. The term xe2x80x9cclosed volumexe2x80x9d is intended to designate a volume of any desired shape delimited by walls tight to liquids and to gases. This volume is arranged inside the tank and communicates with the valve by means of the venting pipe, one end of which is connected to the valve. The function of this volume is to form a capacity capable of connecting and retaining any possible entrainments of liquid coming from the tank which would have passed through the barrier of the valve.
The size of the volume of this capacity is selected to be sufficient to collect all the liquid entrainments capable of passing through the barrier of the valve under special circumstances, particularly when the tank is full or near its maximum filling level. This volume also depends on the dimensions of the valve, on its very design and on the diameter of the pipe connecting it to the latter.
According to the invention, the closed volume internal to the tank and functioning as a capacity of the venting system comprises an emptying device. The term xe2x80x9cemptying devicexe2x80x9d is intended to designate a valve which is located at a low point of the capacity and which can open when a sufficient weight of liquid has been connected in this capacity and which communicates directly with the internal volume of the tank. The function of this emptying device is to recycle the liquid which has been entrained together with the gases emerging from the tank and to prevent the capacity from being filled beyond a predetermined maximum level which depends on the shape of this capacity and on the characteristics of the valve.
According to the invention, the float valve is located outside the volume of the capacity. It may equally be located in the immediate vicinity of the capacity or, on the contrary, be located in a region of the tank which is distant from the said capacity. In either event, however, the float valve is connected to the capacity by means of the venting pipe described above.
According to a first advantageous embodiment of the venting system according to the invention, the latter comprises an overfilling prevention device (abbreviated to xe2x80x9cISRxe2x80x9d). The function of the ISR device is to fix the useful volume of the tank and, during the filling operation, to prevent a predetermined level of liquid in the tank from being exceeded.
The ISR device according to this embodiment may be selected from all the known devices for performing this function. The particular ISR device having a high-density ball which by gravity shuts off the gas outlet pipe of the capacity has given good results.
Preferably, the ISR device is housed in the upper part of the capacity, on the inside of the latter.
According to an advantageous embodiment of the venting system, the capacity emptying device consists of a diaphragm valve which closes a port located at a low point of the capacity. A diaphragm made of elastomeric material and in the shape of an overturned umbrella has given excellent results.
This diaphragm-type emptying device may also advantageously be combined with the particular embodiment of the ISR device housed in the upper part of the capacity described above.
According to a variant of the venting system according to the invention, the float valve surmounts a high-density ball device resting in a perforated well and having the function of causing the closing of the valve in the event of the tank being overturned. This device thus performs a function of closing the tank automatically as soon as the latter begins to be overturned (a function abbreviated to xe2x80x9cROVxe2x80x9d or xe2x80x9croll-over valvexe2x80x9d).
Advantageously, this variant is associated with the particular venting system which comprises an ISR device housed in the upper part of the capacity, as described above.
Another variant to the particular embodiment of the venting system comprises incorporating a device performing the ROV function within the capacity, in a cage, the bottom of which is in the form of a perforated well in which rests a high-density ball which, when it is displaced, pushes upwards a valve capable of shutting off the outlet pipe. This valve may, for example, take the form of a plate carrying, at its centre, a protuberance which can cooperate with the inlet of the gas discharge pipe so as to effect leaktight closure when it is displaced upwards under the effect of the displacement of the ball and comes into contact with the inlet of this pipe.
This variant is suitable in the case of venting systems comprising an ISR device housed in the upper part of the capacity. In this case, the outlet pipe leads directly to the ISR device.
A second embodiment of the venting system according to the invention comprises placing an ISR device at a point on the venting pipe which connects the float valve to the capacity, upstream of the latter. The term xe2x80x9cupstreamxe2x80x9d is intended to designate a location on the side from which the gases come when they escape from the tank. In this configuration, the ISR device is located in the gas pipe, between the valve and the capacity.
According to a variant of the venting system according to the invention, the emptying of the capacity takes place via the orifice of a second float valve which is mounted below the capacity and the float of which slides in a stem submerged in the tank and opens a valve formed by the cooperation of a needle integral with the float and of an orifice located in the bottom of the said capacity.
This variant is highly suitable for the venting systems of the second embodiment described in detail above, that is to say those which comprise an ISR device located at a point of the venting pipe connecting the float valve to the capacity.
In another embodiment of the venting system according to the invention, a device ensuring an ROV function may be arranged at a point on a pipe connecting the capacity to a canister, downstream of the said capacity. The term xe2x80x9cdownstreamxe2x80x9d is intended to mean, in accordance with the meaning of the term xe2x80x9cupstreamxe2x80x9d defined above, a location on the side towards which the gases are directed when they escape from the tank.
In this embodiment, the device ensuring the ROV function participates in the same principle as that described above. It may comprise any system capable of ensuring an identical or equivalent function. In particular, it may comprise a high-density ball device resting in a perforated well, as described above with regard to the first embodiment.
In particular, this embodiment is highly compatible with the second embodiment described above. Even more particularly, this embodiment is advantageously compatible with the venting system comprising an ISR device located at a point on the venting pipe connecting the float valve to the capacity and in which the emptying of the capacity takes place via the orifice of a second float valve mounted below the latter, as described above.
As a variant, a device ensuring an ROV function may also be incorporated into the capacity, in the upper part of the latter. Preferably, the ROV function is ensured by a high-density ball device resting in a cage, the bottom of which is in the form of a perforated well, so that when the ball is displaced, it pushes upwards a valve capable of shutting off the gas outlet pipe leading to a canister.
In particular, this variant is highly compatible with the second embodiment described above. Even more particularly, this variant is advantageously compatible with the venting system comprising an ISR device located at a point on the venting pipe connecting the float valve to the capacity, and in which the emptying of the capacity takes place via the orifice of a second float valve mounted below the latter, as described above.
Another variant of the venting system according to the invention is to use two high-density ball devices, the first arranged below the main float valve and the second below the float valve which shuts off the bottom of the capacity. The term xe2x80x9cmain float valvexe2x80x9d designates the first valve which the gases encounter when they escape from the tank.
In particular, this other variant is highly compatible with the second embodiment described above. Even more particularly, this other variant is advantageously compatible with the venting system comprising an ISR device located at a point on the venting pipe connecting the float valve to the capacity, and in which the emptying of the capacity takes place via the orifice of a second float valve mounted below the latter, as described above.
Preferably, the pipes terminating at or leaving the capacity are integral with the tank. They may be fastened to the tank by any known technique, such as snap-fitting, adhesive bonding, welding, etc. It is particularly preferable that they be welded to the tank or that they form an integral part of the walls of the latter, for example when they are formed at the same time as the tank, during the operations of manufacturing the latter.
Most preferably, these pipes are, furthermore, integral with the various specific members which they connect (valve, capacity, canister, and, if appropriate, ISR and/or ROV devices). The best results are obtained when they are welded to these members or else when they are manufactured so as to form one and the same complex object comprising the tank, the pipes and all the members.
The subject of the present invention is also the use of the venting system described above for venting a fuel tank in a motor vehicle.